I have no clue how they are sized...I think someone at either Candlebrew or Candle Loft, broke down sizes, maybe Kat can fill in that part..
I got my first hemp from an Ebay seller...She just sells them as 6" hemp core wicks.
She also has 5" and 3", but they do not burn as hot as the ones she sells as 6".

I only use straight up and down jars and tins, so I don't know where to even start for hex, I'm sorry. :(